1. Field of the Invention
This invention relates to a crash sensor suitable for use for the detection of crash of a vehicle with a triggering system of a passenger protecting apparatus such as an air bag.
2. Description of the Prior Art
Conventionally, crash sensors suitable for use for the detection of crash of a vehicle with a triggering system of a passenger protecting apparatus such as an air bag are divided into two types including a first type which employs a sensing mass and a second electronic type which employs an accelerometer. As a crash sensor which belongs to the electronic type, a crash sensor is already known which time integrates an acceleration waveform from an accelerometer and causes a passenger protecting apparatus such as an air bag to trigger its operation when the time integrated value exceeds a predetermined value. One of such crash sensors is disclosed, for example, in U.S. Pat. No. 3,701,903. A modified crash sensor is disclosed in U.S. Pat. No. 3,911,391. Wherein, before time integration is performed, a predetermined acceleration is subtracted from an acceleration waveform so that the passenger protecting apparatus may not be rendered operative when an acceleration waveform of such a degree as will not hurt a passenger is inputted such as when the vehicle rides on a rough road.
With the crash sensor, however, operation of the passenger protecting apparatus cannot always be triggered within a required period of time in all forms of crash which are forecast with an actual vehicle. Particularly, decelerations upon head-on crash in a low speed region which does not require the passenger protecting apparatus and upon oblique crash or pole crash in a high speed region in which the passenger protecting apparatus is required are very similar to each other and cannot be identified from each other at an initial stage of crash until operation of the passenger protecting apparatus is triggered. In particular, as seen in FIG. 9, an acceleration waveform (shown by a broken line curve) upon such low speed head-on crash as does not require triggering of operation of the passenger protecting apparatus and another acceleration waveform (shown by a solid line curve) upon oblique crash or pole crash in a high speed region upon which triggering of operation of the passenger protecting apparatus is required are very similar to each other at such a period of time at an initial stage of crash as given as a section from 1 to 2 in FIG. 9 in which it must be determined whether or not operation of the passenger protecting apparatus should be triggered. Accordingly, as shown FIG. 10, it is difficult to identify them from each other even with a crash sensor wherein a predetermined acceleration is subtracted from an acceleration waveform and then the difference thus obtained is time integrated (V1'). As a result, if priority is given to a triggering requirement, unnecessary triggering of operation will take place in a low speed region. On the contrary, if priority is given to a no triggering requirement, a delay or lack in triggering will take place upon high speed oblique crash or pole crash.